<strong>James Thornton</strong>, Chief executive, ClientEarth

What if the polar bears were sick of drowning in melting ice and decided it was time to do something about global warming? How could they best confront the bosses of multinationals whose power plants pollute the atmosphere? By hiring a damn good lawyer to fight in the courts for the law to be changed or enforced and for the emissions to be stopped, that's how. And that man would be James Thornton.

This quiet American's work usually involves lobbying and legal argument, but Thornton, the founding chief executive of a new legal charity called ClientEarth, has already scored dramatic victories over polluters and despoilers in the United States and now wants to do the same in Europe. The aim is to help write new laws - but also, crucially, to ensure that governments keep to the ones they have already agreed, often in a blaze of green glory, and then forgotten about or found too hard to implement.

Thornton works from the notion that his client is the earth itself. Most lawyers would swiftly object: the earth has no money. But Thornton is backed by the philanthropists Michael and Winsome McIntosh, heirs to a supermarket fortune, who have been bankrolling challenges to governments for decades. Based in London, ClientEarth recently opened offices in Brussels and Warsaw, too. It makes little fuss: the head office near a London Tube station is hard to identify, and Thornton turns out to be a balding 54-year-old in a grey suit who speaks softly and practises Zen Buddhism.

His first big effort in Britain has been to challenge plans for two new coal-fired power plants at Kingsnorth in Kent, where the Climate Camp was held last summer. "Protest is a good thing," he says, "but the law is a powerful tool to use alongside it." The weapon ClientEarth has chosen is the Strategic Environmental Assessment. The government has a legal duty to carry one out at Kingsnorth, says Thornton, who believes it would expose the "potentially devastating environmental consequences" of allowing a new generation of coal-fired plants to be launched without carbon capture.

ClientEarth's other current projects include challenging France to enforce an existing EU ban on drift-net fishing, while attempting to establish the legal right of European citizens to bring such cases at all.

Born in New York, he was the son of a law professor at the University of Notre Dame. "We grew up practising the Socratic method at the dinner table," he says. After Yale, he worked on Wall Street, then joined the "intriguingly eccentric" National Resources Defence Committee, a group of radical young lawyers recruited by the McIntoshes. Thornton targeted the Clean Water Act, which was ignored by the Reagan administration. Companies were being allowed to get away with not declaring what they were pumping out. "They thought they could violate the heck out of the rivers and seas and get away with it." His team took 60 cases to federal courts in six months and won them all. The government started enforcing the law.

Thornton's next great fight was in California, where he protected 350,000 acres of unspoiled country, armed only with a gnatcatcher. The threat of being sued on behalf of this little bird, if its environment was destroyed, persuaded developers to preserve swaths of coastal land. "The right law, properly used," he says, "can level the playing field."

ClientEarth has already attracted celebrity supporters in the UK: Brian Eno, a patron, put the organisation in contact with the band Coldplay. "Coldplay have something like a million friends through Facebook and so on," says Thornton. "They are going to introduce their friends to membership of ClientEarth. When we bring lawsuits, we will then represent a great many people all over Europe."

The ideal behind all this, for Thornton, is wild law, or earth jurisprudence: that all living things should have rights equivalent to those enjoyed by human beings, to be considered whenever resources are being exploited. Hence the militant bears. "A legal action could be brought on their behalf, as it might be for a child, to prevent damage to their environment."

For now, Thornton must act for Planet Earth by representing humans in court, case by case. He is a patient man who will be ordained a Zen priest this year, after 25 years of practice - but he knows that small shifts in the law can change the world in a very big way.